The Combining CS and IMS services (CSI) are a research subject of great concern in the 3rd Generation Partnership Project (3GPP) standard. This research subject aims at combining Circuit Switch (CS) domain services and IP Multimedia Subsystem (IMS) domain services in the 3G.
The primary research topic in the CSI phase 1 aims at correlating a CS domain call of a CS IMS dual-mode UE with an IMS session. Due to the limitation in bearing capacity, a CSI phase 1 UE utilizes in precedence the CS to bear real-time voice services.
Unless otherwise specified, the CSI UE mentioned hereinafter refers to the CSI phase 1 UE. During the interworking between the CSI UE and the IMS UE, there exists such a situation that if the IMS UE calls the CSI UE through IMS signaling to establish a voice session, the IMS session directly reaches the IMS part of the CSI UE, and an IMS voice session is established directly between these two UEs after the CSI UE receives the request message. However, due to limits of QoS and the like of the IMS at the CSI UE side, the CSI UE would preferably establish a real-time voice session through the CS.
FIG. 1 shows a framework for interworking between the CSI UE and the IMS UE in the prior art (3GPP TS 23.002 Network Architecture).
The following technologies relate to the subject on the implementation of the interworking between the CSI UE and the IMS UE.
An interworking control function is arranged at the CSI UE side. Upon the receipt of a session request from the IMS UE, the interworking control function separates the session message involving a variety of media components according to the relevant information, divides the session into a session containing a real-time media component and a session containing a non-real-time media component, then makes a determination according the relevant information to terminate the real-time session in the CS domain and terminate the non-real-time session in the IMS. The framework of this technical scheme is shown in FIG. 1, and the process includes the following steps.
At step S102, a Voice over IP (VoIP) UE initiates a request (e.g., an Invite) for an IMS session to a CSI UE, with the request containing real-time service information and non-real-time service information.
At step S104, the IMS (including the MGCF/MGC, S-CSCF, etc.) at the VoIP side forwards the request to the CSI-Interworking (CSI-IW).
At step S106, the CSI-IW carries out service logical processing and separates the session request according to the relevant information.
At step S108, a session request is sent to the CSI UE by the CSI-IW. The request message contains non-real-time service information and indication information instructing the CSI UE to initiate a CS bearing from the CSI UE to the network.
At step S110, upon the receipt of the session request message, the CSI UE initiates a CS call (e.g., a SETUP request) to the CSI-IW.
At step S112, the Media Gateway Control Function (MGCF) receives the CS call request from the CSI UE, maps the CS call request into an INVITE, and sends the INVITE to the CSI-IW.
At step S114, the CSI-IW sends a 200 OK response to the MGCF.
At step S116, the MGCF maps the 200 OK response into a CS CONNECT message to be sent to the CSI UE.
At step S118, the CSI UE sends a 200 OK response which contains only non-real-time media information (e.g. an MSRP message).
At step S120, the CSI-IW combines the CS call from the CSI UE with the IMS session.
At step S22, the CSI-IW sends a 200 OK response after the combination to the called IMS.
At step S124, the called IMS forwards the 200 OK response to the VoIP UE.
However, a session change during interworking between the CSI UE and the IMS UE may be desired, while the architecture and the process in the prior art provide no solution to session changing during interworking between the CSI UE and the IMS UE in the packet network.
Therefore, a solution to address the issue of session changing during interworking between the CSI UE and the IMS UE in the prior art is desired.